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I have a 2004 x3 and the remote key no longer works. It was working on and off for about a few weeks and now, nothing. It won't set the alarm, open trunk,or open doors. So the question is.... will reprogramming work and if so how do I do that? Or is it the battery, and can I replace it? I know that its rechargable every time you drive. Has anyone else had this problem?!?

I have a 2004 x3 and the remote key no longer works. It was working on and off for about a few weeks and now, nothing. It won't set the alarm, open trunk,or open doors. So the question is.... will reprogramming work and if so how do I do that? Or is it the battery, and can I replace it? I know that its rechargable every time you drive. Has anyone else had this problem?!?

Sounds like you have mislaid your 2nd. rechargeable key (or bought used, and did not get the full complement).

Having the 2nd. one would allow you confirm whether the problem was with the key, or the car.

If it is a battery problem, some people have successfully done it on a 3 series - but not for the fat-fingered.

All of the above. There has been successful replacement of the battery in the X3 keys as well, with a radio shack battery. The poster (with a very detailed DIY photo sequence) alluded to the fact that (as I recall) getting the key head apart was the hardest part. It was awhile back, I believe. It does need to be soldered in, not just a drop in change.

This, from the E39 bestlinks, can also help others, so I post it here for reference:
- How to replace the old-style BMW square key battery (1) (2) & how to replace the rubber key pads in the square keys (1) (2) & what the red LED indicates on the old square key (1) & what can go wrong with a key and where to send it for repair (1) (2) (3) (4) & what battery to use in the new style 2000+ BMW E39, E46, E53, E85, etc. diamond key (1) (2) (3) (4) (5) (6) (7) & youtube videos of diamond key repairs (1) (2) (3) & a square key to diamond key retrofit and transponder swap (1) (2) (3) (4) & diamond key to square key retrofit questions (1) & how to recharge your key out of your BMW and how long that key will last in the drawer before it needs that off-the-car recharging (1) & the details on swapping the BMW diamond key transponder (1) & the proper diamond key initializing or programming sequence (1) (2) (3) (4) (5) (6) & what to do if your only key is locked inside your bimmer (1) & a description of the various types of BMW Remote, Illuminated, Spare/Wallet, & Valet/Service keys (1) (2) & a list of diamond key EWS, FZV, & DWA functions (1) (2) & all about the 10-key limit to programming your own keys at home (1) & a description of the ignition key ISN (individual serial number) ten-second rule (1) & what to do if you lost your only diamond key (1) or what to do if your BMW key was stolen (1)